Capstone: build an agent without a framework

def run(question: str, model, max_steps: int = 6, max_tokens: int = 30_000, log=print) -> str:
    messages = [{"role": "user", "content": question}]
    used = 0
    for step in range(1, max_steps + 1):                        # stop condition: step limit
        calls, tokens = model.next_calls(messages)
        used += tokens
        if not calls:
            return "Stopped: the model answered without calling finish."
        results = []
        for call in calls:                                       # run every call from this turn
            try:
                output = TOOLS[call.name](**call.input)
                ok = True
            except Exception as e:                               # errors go back to the model
                output, ok = {"error": str(e)}, False
            log(f"step {step}: {call.name}({json.dumps(call.input)}) -> {json.dumps(output)}")
            if call.name == "finish" and ok:                     # stop condition: task done
                return output["answer"]
            results.append({"type": "tool_result", "tool_use_id": call.id,
                            "content": json.dumps(output), "is_error": not ok})
        messages.append({"role": "user", "content": results})  # all results in ONE message
        if used > max_tokens:                                    # stop condition: budget
            return "Stopped: token budget used up."
    return "Stopped: step limit reached without an answer."

cd examples/mini-agent
pytest -q
python agent.py
AGENT_PROVIDER=anthropic python agent.py "Cost of 2 nights in Porto plus a 150 GBP train?"

.....                                                                    [100%]
5 passed in 0.01s
step 1: hotel_price({"city": "Lisbon", "nights": 3}) -> {"city": "Lisbon", "nights": 3, "total_gbp": 285}
step 2: calculator({"expression": "285 + 400"}) -> {"result": 685}
step 3: finish({"answer": "About 685 GBP: 285 for 3 hotel nights plus the 400 flight."}) -> {"answer": "About 685 GBP: 285 for 3 hotel nights plus the 400 flight."}
answer: About 685 GBP: 285 for 3 hotel nights plus the 400 flight.